A focal plane array is an image sensing device where pixels are positioned at the focal plane of a lens. Focal plane arrays are used in various types of applications, including air-to-air missiles and anti-tank missiles where the arrays are used as infrared sensors. In these types of applications, it is often necessary or desirable to maintain the temperature of a focal plane array at a particular temperature or within a very narrow temperature range.
Variable-flow Joule-Thomson cryostats are often used to cool very large focal plane arrays in these types of applications. However, these cryostats can suffer from various drawbacks. For example, these cryostats can be quite inefficient in their use of coolant gas, and they can be very unstable in controlling the temperatures of focal plane arrays. Moreover, these cryostats are prone to clogging, which interrupts their normal operation. In addition, some attempts have been made to incorporate shape memory metal actuators into Joule-Thomson cryostats, but those actuators are slow and imprecise. Any failure or other shortcoming of a cryostat can interfere with the proper operation of air-to-air missiles, anti-tank missiles, and other ordnance.